a. Field of Invention
The invention relates to guidance systems and methods and, more particularly, to an improved ground collision avoidance system (iGCAS) inclusive of a hardware architecture and software in which a robust array of collision avoidance processes are functionally partitioned into separate software modules. Collectively, the iGCAS modules autonomously determine when a ground collision is imminent, what maneuver should be used to avoid the predicted ground collision, and when the maneuver should be initiated and terminated. The avoidance maneuver may be executed automatically by an autopilot system or signaled to the pilot for manual execution.
b. Background of the Invention
Controlled Flight into Terrain (CFIT) occurs when properly functioning aircraft under the control of qualified crew are inadvertently flown into terrain. CFIT is a leading cause of aviation fatalities for non-commercial air-carriers, causing an estimated 100 fatalities per year in the U.S. The problem was conformed by several studies in the 1970s and since then the U.S. National Transportation Safety Board (NTSB) has mandated some form of ground proximity warning system (GPWS) on larger aircraft. Smaller turboprop airplanes were thought less susceptible to such accidents, but subsequent studies found that many small aircraft accidents could have been similarly avoided with GPWS equipment. Early GPWS used the downward looking radio altimeter to determine height above ground and rate of closure to determine if an aircraft was in a potentially hazardous situation. Subsequent improvements incorporated limited situational awareness (e.g. landing gear deployment) and ILS glideslope deviation warnings.
More recent advances in terrain mapping technology have led to the development in the late 1990s of an enhanced ground proximity Warning System (EGPWS) that combines accurate positional knowledge (normally determined from GPS) with a three dimensional map of surrounding terrain to identify ground-flight path conflict ahead of the aircraft and generate audio and visual warnings to the flight crew when certain parameters are breached. The FAA refers to EGPWS systems as Terrain Awareness and Warning Systems (TAWS), while others still use the more generic term “GPWS”. TAWS improves on the earlier GPWS systems by providing the flight crew much earlier aural and visual warning of impending terrain, forward looking capability, and continued operation in the landing configuration. Currently, all U.S. registered turbine-powered airplanes with six or more passenger seats (exclusive of pilot and copilot seating) must be equipped with an FAA-approved TAWS system.
Parallel to commercial aviation, the U.S. Defense Department developed TAWS functionality for military implementation. Early DoD systems focused on altitude clearance and used radar and barometric altimeters to give clearance plane and descent after takeoff warnings. Next generation systems incorporated navigation information from radar, radio navigation, GPS and inertial navigation systems to determine the three dimensional position relative to the earth based on digital terrain elevation databases to create a predictive warning system. The Navy provided TAWS capability in the F/A-18 aircraft in 2004, and the Air Force separately developed and deployed its Predictive Ground Collision Avoidance System (PGCAS) in the F-16. PGCAS functions by establishing the aircraft's position relative to the surrounding terrain as mapped in the Digital Terrain System (DTS). DTS scans a corridor and develops a “worst case” two dimensional terrain-obstacle profile from the data in the corridor and PGCAS provides pilot advisories for terrain located within at least 10 seconds time of flight from the aircraft. The PGCAS algorithm provides inputs to the F-16 core avionics computers which generates HUD, MFDS, and VMU advisories to the pilot when the aircraft trajectory penetrates the pilot-selectable Minimum Terrain Clearance (MTC) setting, obstacles included
By way of example, U.S. Pat. No. 5,839,080 to Muller et al. (assigned to Allied Signal) discloses a terrain awareness system (TAS) that provides LOOKAHEAD/LOOK-DOWN as well as LOOK-UP terrain advisory and warning indications to the pilot of an aircraft of a hazardous flight condition. This system employs an airport data base, GPS, and a terrain data base having various resolutions depending on the topography of the particular geographic area of interest, and provides terrain advisory and the warning signals as a function of the flight path of the aircraft.
U.S. Pat. No. 6,826,459 to Conner et al. (assigned to Honeywell) discloses a ground proximity warning system, method and computer program product that controllably alter the base width of the alert envelope in order to accommodate uncertainties associated with the current position of the aircraft.
U.S. Pat. No. 7,205,906 to Johnson et al. (assigned to Honeywell) discloses a system, method and computer program product for reducing nuisance warnings during low altitude flight conditions and in the presence of low position uncertainty. The system includes a first component that determines whether the aircraft is in a low altitude flight condition and a second component that determines the position, positional uncertainty, and the heading. The system also includes a third component that attenuates and refines the look-ahead envelope in accord with the determined condition of flight and positional uncertainty.
U.S. Pat. Nos. 7,236,104 and 7,257,487 to Tran (assigned to Honeywell) disclose a hybrid air collision avoidance system (HACAS), an air collision avoidance system with extended existing air avoidance capabilities and incorporated with new hybrid capabilities to perform hybrid air collision prediction and hybrid air collision avoidance.
U.S. Pat. No. 7,337,043 to Bull (assigned to Rockwell Collins) discloses a terrain advisory system for an aircraft. The TAWS generates cautions and alerts. The processing unit includes a program that generates a terrain advisory envelope extending beyond the distance and lateral envelope within which the TAWS provides cautions and alerts.
U.S. Pat. No. 7,693,618 to Johnson et al. (assigned to Honeywell) discloses a system and method for monitoring Required Navigational Performance (RNP) Procedures and reducing nuisance Enhanced Ground Proximity Warning System warnings.
U.S. Pat. No. 7,881,866 to Meunier et al. (assigned to Thales) discloses a Terrain Awareness and Warning System that produces a new “Too Low Terrain” predictive alert of “Caution” type when the crew of the aircraft has the possibility of resolving a detected risk of collision with the terrain without interrupting the current maneuver to stabilize at a safety altitude by a leveling-off maneuver, without performing a vertical avoidance maneuver.
U.S. Pat. No. 8,049,644 to Oehlert et al. (assigned to Rockwell Collins) discloses a terrain advisory system configured to generate a three-dimensional image.
U.S. Pat. No. 8,249,799 to Flotte et al. (assigned to Thales) discloses a method of presenting zones at risk for an aircraft.
U.S. Pat. No. 8,280,622 to Meunier et al. (Assigned to Thales) discloses a system indicating to a pilot that an aircraft has passed the limit-point of success of a standard vertical avoidance maneuver.
U.S. Pat. No. 8,395,533 to Ganille et al. (assigned to Thales) discloses a method for managing an anticollision system for aircraft comprising means of detecting collision with a threat and at least one head-up viewing device. The symbol system comprises two display modes dedicated to collision detection which are: on the one hand an “action” mode—a potential collision is detected by the system, the symbol system comprises at least one symbol representative of the limits of the disengagement path of the aircraft to avoid the collision and enabling the pilot to engage his avoidance maneuver, and on the other hand a “control” mode—this mode is displayed when the avoidance maneuver is engaged and the collision avoided.
United States Patent Application 20130191016 by Baillon et al. (Thales Neuilly-sur-Seine) published Jul. 25, 2013 shows a Method and Device for the Filtering of Alerts Originating from a Collision Detection System of an Aircraft during runway approach. Apparently, current onboard terrain detection systems are disabled as soon as the aircraft is situated in the environs of an airport, and cannot warn of abnormal drops in the case of a CFIT (controlled flight into terrain). The '1016 application analyzes angle of descent for the landing runway, altitude of the aircraft, distance to the runway, and speed vector, and authorizes the output of a terrain warning alert in an abnormal drop situation even though all landing envelope conditions (horizontal and vertical convergence) are met.
All the foregoing TAWS improvements provide more time for flight crew to take corrective action, but still suffer from several shortcomings. TAWS only alerts the unaware pilot to a problem but fails to advise the pilot on how to get out of the problem. Moreover, TAWS systems are highly susceptible to providing too many false warnings. This tends to lull pilots into ignoring valid warnings when they come, or even worse, turn the system off.
With this as a baseline, the system disclosed herein proposes several improvements over currently implemented commercial (Class A) and general aviation (Class B) terrain awareness and warning systems (TAWS), including an improved collision avoidance algorithm fidelity, throughput enhancements including trajectory modeling and terrain handling, and display enhancements for presenting multi-trajectory escape options. The multiple improvements not only avoid false warnings and provide more time for flight crew to take corrective action, but also advise the pilot on how to get out of a problem. In contrast to the prior art, this tends to encourage pilots to pay attention to all warnings when they come and never turn the system off.